1. Field
The present disclosure relates generally to airfoils for use with wind-powered vehicles, and more particularly to a reversible camber soft wing sail.
2. Background
Conventional single surface sails made out of thin materials provide limited performance, especially in high wind conditions. Other more complex designs have therefore been proposed to form sails into an airfoil shape similar to the shape of an airplane wing. The same aerodynamic principles that apply to horizontal aircraft wings also apply when the wing is positioned vertically on end. When used by wind-powered vehicles such as sailboats, windsurfing boards, etc., these vertical airfoils are often referred to as wing sails.
Wing sails differ from conventional sails in that they have two surfaces of curvature rather than a single thin surface. The two surfaces create a pressure differential by forcing air to flow past them at different velocities, thereby creating lift. As a result, high lift airfoils are asymmetrical and only generate lift efficiently in one direction. This presents a challenge for various sailing applications, where the sail's airfoil camber is required to reverse in order to tack. Conventional sails are able to reverse due to the flexibility of their material. However, tacking in this manner is more difficult with a wing sail due to its thicker, three dimensional shape.
Numerous wing sail designs with unique configurations have been developed, but each has had its own drawbacks and shortcomings Examples include two ply sails wrapped around a spar or filled with foam padding, wings with asymmetrical but fixed chordal profiles, symmetrical sails with inflatable media between two plies, and others. Prior designs such as these are often too complicated for production and difficult to operate.
Accordingly, there remains a need in the art for improved wing sails capable of offering the advanced aerodynamic performance of an airfoil while being user-friendly and cost-effective to manufacture.